Power factor correction apparatus

ABSTRACT

A power factor correction (PFC) apparatus is disclosed. The apparatus comprises a DC rectification circuit and a PFC auxiliary circuit. In this apparatus, the PFC auxiliary circuit is coupled between the input and output terminals of the DC rectification circuit. According, not only can the conduction time be increased, but the working current peak is restrained. Thus, the increased size of the choke and inductance of the inductor can be prevented.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 94105353, filed on Feb. 23, 2005. All disclosure of theTaiwan application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power factor correction (PFC)apparatus, and more particularly to a passive PFC apparatus forimproving power factors.

2. Description of the Related Art

Power factor reflects the relation between effective power and apparentpower consumption of electricity. It is defined as the ratio of theeffective power to the apparent power (VA, or voltage multplyingcurrent). Basically, a power factor can be used to measure theefficiency of electricity usage. The higher the power factor, the lowerthe AC source current, and thus the better the electricity usageefficiency. The circuit operational principle of a power factorcorrection (PFC) circuit in a power supply is to control and adjustphase and the shape of waveform of the input alternating current (AC) asclose as possible to the AC voltage waveform, and ideally to make thepower factor close to 1. This is very important for electronic deviceswhich require high electricity, or the electricity consumed by theelectronic device may exceed the power source current capability.

Generally, PFC circuits include active PFC circuits and passive PFCcircuits. An active PFC circuit is composed of a control circuit of anactive device and a power switches. In its operational principle, theinput current waveform is adjusted to make it as similar to the inputvoltage waveform as possible. The power factor of the active PFC circuitcan be close to 100%.

A passive PFC circuit, however, is composed of passive components suchas inductors and capacitors. Due to its low-frequency input current,usually from 50 Hz to 60 Hz, a conventional passive PFC circuit requiresa big inductor and its power factor is only from about 75% to about 80%.Because of its complicated control circuit, the active PFC circuit,compared with the passive PFC circuit, has higher manufacturing costs.Based on the cost consideration, the passive PFC circuit still is apreferred choice.

FIG. 1 is a circuit diagram showing a conventional passive PFC choke inan application of a typical bridge rectification circuit. Referring toFIG. 1, the passive PFC circuit comprises an inductor L1, a bridgerectifier B1 and a capacitor C1. The AC voltage source V1 is receivedand processed by the PFC circuit, and the stable DC voltage is obtainedto drive the load represented by a resistor R1.

FIG. 2 is a drawing of signal waveform variations of a conventionalpassive PFC circuit. In the following, the waveform variations of theFIG. 2 based on the passive PFC circuit in FIG. 1 are discussed. In thebottom of FIG. 2, the AC voltage Vin1 is the AC voltage provided by theAC voltage source V1. After the operation of the passive PFC circuit,the stable DC voltage Vout1 is output to drive the resistor R1. In thetop of FIG. 2, the current I1 in dotted line is the current provided bythe AC voltage source V1; the current IL1 in solid line is the workingcurrent of the inductor L1. In order to describe the variations of thecurrents I1 and IL1 in detail, the currents IL1 and I1 are shown withreverse current directions in this figure.

The passive PFC circuit of this structure requires a large size andinductance for the inductor L1 to increase the conduction time of theinductor L1 and restrain the peak current of the working current IL1 ofthe inductor L1, thereby controlling the charging current of thecapacitor C1. However, to increase the size and the inductance of theinductor L1, the charging time of the capacitor C1 is delayed. As aresult, the capacitor C1 cannot fully charged to the peak voltage of theinput AC voltage. This will become worse for the higher powerapplication where a higher value of bulk capacitor C1 is used.

SUMMARY OF THE INVENTION

Accordingly, the present invention is related to a power factorcorrection (PFC) apparatus. In the apparatus, a PFC auxiliary circuit iscoupled between the input and output terminals of the conventionalpassive PFC circuit so that a smaller size and inductance of theinductor can be used.

The present invention provides a PFC apparatus. The PFC apparatus iscoupled to an alternating current (AC) source, and receives the ACvoltage therefrom. The PFC apparatus comprises a DC rectificationcircuit, a PFC auxiliary circuit and a load. Wherein, the DCrectification circuit receives the AC voltage and outputs a directcurrent (DC) voltage based on the AC voltage. An input terminal of thePFC auxiliary circuit is electrically coupled to a positive AC inputterminal of the AC source, while an output terminal of the PFC auxiliarycircuit is electrically coupled to the first terminal of the load toprovide part of the working current of the load. A first terminal of theload described above is coupled to a first output terminal of the DCrectification circuit. A second terminal of the load is coupled to asecond output terminal of the DC rectification circuit.

According to the PFC apparatus of an embodiment of the presentinvention, the DC rectification circuit comprises a first inductivereactance device, a bridge rectifier and a second reactance (capacitive)device. Wherein, a first terminal of the first inductive reactance iscoupled to the positive AC input terminal of the AC source. A firstterminal of the bridge rectifier described above is coupled to a secondterminal of the first inductive reactance device. A second terminal ofthe bridge rectifier is coupled to a negative AC input terminal of theAC source. A first terminal of the second reactance device describedabove is coupled to a third terminal of the bridge rectifier. A secondterminal of the second reactance device is coupled to a fourth terminalof the bridge rectifier.

According to the PFC apparatus of an embodiment of the presentinvention, the first terminal of the load described above iselectrically coupled to the first terminal of the second reactancedevice, and the second terminal of the load is electrically coupled tothe second terminal of the second reactance device.

According to the PFC apparatus of an embodiment of the presentinvention, the PFC auxiliary circuit is a resonant circuit. The resonantcircuit comprises a third reactance (inductive) device and a fourth(capacitive) reactance device. Wherein, a first terminal of the thirdreactance device described above is coupled to the positive AC inputterminal of the AC source. A first terminal of the fourth reactancedevice described above is coupled to a second terminal of the thirdreactance device. A second terminal of the fourth reactance device iscoupled to the first and the second output terminals of the DCrectification circuit via a second rectification circuit, diode D1 andD2 (306) respectively.

According to the PFC apparatus of an embodiment of the presentinvention, the PFC auxiliary circuit further comprises a second DCrectification circuit. A first terminal of the second DC rectificationcircuit is coupled to the second terminal of the fourth reactance, asecond terminal of the second DC rectification circuit is coupled to thefirst output terminal of the DC rectification circuit, and a thirdterminal of the second DC rectification circuit is coupled to the secondoutput terminal of the DC rectification circuit.

According to the PFC apparatus of an embodiment of the presentinvention, the second DC rectification circuit further comprises asecond diode. A first terminal of the second diode is coupled to thefirst terminal of the DC rectification circuit and a second terminal ofthe second diode is coupled to the second output terminal of the DCrectification circuit.

Accordingly, in the PFC apparatus of the present invention, a PFCauxiliary circuit is coupled between the input and output terminals ofthe DC rectification circuit to increase the conduction time of theinput current and restrain the input working current peak. Thus, theproblems of increasing the size of the choke and the inductance of theinductor are prevented.

The above and other features of the present invention will be betterunderstood from the following detailed description of the preferredembodiments of the invention that is provided in communication with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a conventional passive PFC circuit.

FIG. 2 is a drawing showing signal waveform variations of a passive PFCcircuit.

FIG. 3 is a schematic circuit drawing of a complete PFC apparatusaccording to an embodiment of the present invention.

FIGS. 4 and 5 are schematic circuit drawings of PFC apparatusesaccording to other embodiments of the present invention.

FIG. 6 is a drawing of a waveform of signal variations of a PFCapparatus according to an embodiment of the present invention.

DESCRIPTION OF SOME EMBODIMENTS

The present invention provides a power factor correction (PFC)apparatus. The present invention is characterized in the PFC auxiliarycircuit, which is coupled between the input and output terminals of thetraditional DC rectification circuit to increase the conduction time ofthe input current and restrain the input working current peak, therebypreventing an increased size of the choke and the inductance of theinductor.

FIG. 3 is a schematic circuit drawing of a complete PFC apparatusaccording to an embodiment of the present invention. Referring to FIG.3, the passive PFC circuit 300 of this embodiment comprises a DCrectification circuit 301. This circuit has a structure similar to thatof the conventional passive PFC circuit, which is composed of a firstreactance device, such as an inductor L1, a bridge rectifier B1 and asecond reactance device, such as a capacitor C1.

Wherein, the positive AC output terminal of the AC voltage source V1 iscoupled to the first terminal 321 of the inductor L1 through the route341. The second terminal 323 of the inductor L1 is coupled to the firstterminal 325 of the bridge rectifier B1 through the route 343. Thesecond terminal 327 of the bridge rectifier B1 is coupled to thenegative AC output terminal of the AC voltage source V1 through theroute 345. In addition, the third terminal 329 of the bridge rectifierB1 is coupled to the first terminal 331 of the capacitor C1 through theroute 347. The second terminal 333 of the capacitor C1 is coupled to thefourth terminal 335 of the bridge rectifier B1.

After the DC rectification circuit 301 receives the AC voltage suppliedby the AC voltage source V1, a stable DC voltage processed andtransformed by the DC rectification circuit 301 is output to charge thecapacitor C1. The first load 305 is then driven. In this embodiment, thefirst load 305 is a resistor R2.

In the present invention, the PFC auxiliary circuit 304 is coupledbetween the input and output terminals of the DC rectification circuit301. The PFC auxiliary circuit 304 comprises a resonant circuit 303 anda second DC rectification 306. The harmonic circuit 303 comprises thethird reactance device 307 and the fourth reactance device 309. Wherein,the third reactance device 307 is the inductor L2, and the fourth device309 is the capacitor C2 in this embodiment. The resonant circuit 303provides a current path to improve the charging of the capacitor C1 ofthe DC rectification circuit during the continuous periodical variationof the positive and negative waveform of the AC signal. Of course, oneof the ordinary skill in the art would know that the third reactancedevice can be a resistor, for example.

In this embodiment, in order to control the charging current path of thecapacitor C1, the second DC rectification 306 is coupled between thecapacitor C2 of the resonant circuit 303 and the capacitor C1 of the DCrectification circuit 301. The second DC rectification 306 comprisesdiodes D1 and D2. Wherein, the anode of the diode D1 is coupled to thecapacitor C2 through the route 351; the cathode of the diode D1 iscoupled to the capacitor C1 through the route 353. The anode of thediode D2 is coupled to the fourth terminal 335 of the bridge rectifierB1 through the route 355. The cathode of the diode D2 is coupled to thecapacitor C2 through the route 357.

When the AC voltage output from the AC voltage source V1 is the positivehalf cycle, the PFC apparatus has two charging routes for the capacitorC1. Wherein, the first charging route is from the positive AC outputterminal of the AC voltage source V1, through the inductor L1, the firstterminal 325 of the bridge rectifier B1, the capacitor C1, the fourthterminal 335 of the bridge rectifier B1, and the second terminal 327 ofthe bridge rectifier B1, to the negative AC output terminal of the ACvoltage source V1, to complete the first full charging route.

The second charging route is from the positive AC output terminal of theAC voltage source V1, through the inductor L2, the capacitor C2, thediode D1, the first capacitor C1, the fourth terminal 335 of the bridgerectifier B1, and the second terminal 327 of the bridge rectifier B1, tothe negative AC output terminal of the AC voltage source V1, to completethe second full charging route.

When the AC voltage output from the AC voltage source V1 is the negativehalf cycle, the PFC apparatus also has two charging routes for thecapacitor C1. Wherein, the first charging route is from the negative ACoutput terminal of the AC voltage source V1, through the second terminal327 of the bridge rectifier B1, the third terminal 329 of the bridgerectifier B1, the capacitor C1, the fourth terminal 335 of the bridgerectifier B1, the first terminal 325 of the bridge rectifier B1, and theinductor L1, to the positive AC output terminal of the AC voltage sourceV1, to complete the first full charging route, while the AC voltage isthe negative half cycle.

The second charging route, when the AC voltage is the negative halfcycle, is from the negative AC output terminal of the AC voltage sourceV1, through the second terminal 327 of the bridge rectifier B1, thethird terminal 329 of the bridge rectifier B1, the capacitor C1, thediode D2, the capacitor C2, and the inductor L2, to the positive ACoutput terminal of the AC voltage source V1, to complete the second fullcharging route, while the AC voltage is the negative cycle.

From the descriptions above, either the AC voltage of the AC voltagesource V1 is the positive or negative half cycle, the capacitor C1 ischarged through the first or second charging route. As a result, theconduction time of the input voltage can be effectively increased, andthe working current peak of the input current IL1 can be restrained. Thefollowing is how the signals are processed by the circuit according tothe signal waveform variations of the apparatus.

FIGS. 4 and 5 are schematic circuit drawings of PFC apparatusesaccording to other embodiments of the present invention. The significantdifference between the circuits of FIGS. 3 and 4 is that the seriallyconnected inductors L3 and L4 replace the inductor L1 coupled betweenthe AC voltage source V1 and the bridge rectifier B1. Wherein, theinductors L3 and L4 can be a single couple choke. The inductor L3 iscoupled between the third terminal 329 of the bridge rectifier B1 andthe capacitor C1. The inductor L4 is coupled between the capacitor C1and the fourth terminal 335 of the bridge rectifier B1. The signalprocessing in this embodiment is similar to that in FIG. 3.

In addition to the modifications of the circuit in FIG. 4, in thecircuit of FIG. 5, the serially connected capacitors C3 and C4 replacethe capacitor C1, and a switch S1 between the capacitors C3 and C4 iscoupled to the second terminal 327 of the bridge rectifier B1 to controlthe circuit. The signal processing in this embodiment also is similar tothat in FIG. 3. One of ordinary skill in the art would know that theinductors L3 and L4 can be replaced by a single coupled inductor.

FIG. 6 is a drawing of a waveform of signal variations in a PFCapparatus according to an embodiment of the present invention. In thefollowing, the waveform variations of FIG. 6 based on the PFC apparatusin FIG. 3 are discussed. Referring to FIG. 6, the AC voltage Vin2 is theAC voltage provided by the AC voltage source V1 shown in the bottom ofthis figure. After processed by the PFC apparatus of the presentinvention, the stable DC voltage Vout2 is output to drive the resistorR2.

In the top of FIG. 6, the current I1 in dotted line is the currentprovided by the AC voltage source V1. The current IL1 in solid line isthe working current of the inductor L1; the current IL2 in solid line isthe working current of the inductor L2. In order to describe the signalvariations in detail, though having the same direction, the currents IL1and I1 are shown with reverse current directions in this figure.

The signal waveform variations of FIG. 6 are compared with the waveformsignal variations of the passive PFC circuit of FIG. 2. It is obviousthat the conduction time T of the current I1 provided by the AC voltagesource V1 is increased. This is because a charging route is provided inthe resonant circuit 303 coupled in the PFC apparatus either the ACvoltage of the capacitor C2 and the inductor L2 is the positive ornegative half cycle.

Before the capacitor C1 is charged, the inductor L2 is turned on, andthe conduction time I of the current I1 is increased, whereas theconduction time of the inductor L1 is not changed. With the additionalcharging route, the current flowing through the one charging route inthe prior art is divided into two charging routes. Compared with thecurrent peak shown in FIG. 2, the current peak IP shown in FIG. 6 issubstantially reduced. The working current peak thus is restrained.

Accordingly, in the PFC apparatus of the present invention, a PFCauxiliary circuit is coupled between the input and output terminals ofthe DC rectification circuit to provide an additional current path so asto increase the conduction time of the charging current of the circuitand also restrain the input working current peak. Thus, the problems ofincreasing the size of the choke and the inductance of the inductor areprevented, while the circuit performance is improved.

Although the present invention has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be constructed broadly to include other variants and embodimentsof the invention which may be made by those skilled in the field of thisart without departing from the scope and range of equivalents of theinvention.

1. A power factor correction (PFC) apparatus, connecting and receivingan alternating current (AC) voltage output from an AC source, the PFCapparatus comprising: a DC rectification circuit, receiving the ACvoltage and outputting a direct current (DC) voltage based on the ACvoltage; a load, a first terminal of the load being coupled to a firstoutput terminal of the DC rectification circuit, a second terminal ofthe load being coupled to a second output terminal of the DCrectification circuit; and a PFC auxiliary circuit, an input terminal ofthe PFC auxiliary circuit being electrically coupled to a positive ACinput terminal of the AC source, while an output terminal of the PFCauxiliary circuit being electrically coupled to the first terminal ofthe load to provide part of a working current of the load.
 2. The PFCapparatus of claim 1, wherein the DC rectification circuit comprises: afirst reactance device, a first terminal of the first inductivereactance being coupled to the positive AC input terminal of the ACsource; a bridge rectifier, a first terminal of the bridge rectifierbeing coupled to a second terminal of the first reactance device, asecond terminal of the bridge rectifier being coupled to a negative ACinput terminal of the AC source; and a second reactance device, a firstterminal of the second reactance device being coupled to a thirdterminal of the bridge rectifier, a second terminal of the secondreactance device being coupled to a fourth terminal of the bridgerectifier.
 3. The PFC apparatus of claim 2, wherein the first terminalof the load is electrically coupled to the first terminal of the secondreactance device, and the second terminal of the load is electricallycoupled to the second terminal of the second reactance device.
 4. ThePFC apparatus of claim 2, wherein the first reactance device is aninductor.
 5. The PFC apparatus of claim 2, wherein the second reactancedevice is a capacitor.
 6. The PFC apparatus of claim 2, wherein thethird terminal of the bridge rectifier is a positive DC output terminal,and the fourth terminal of the bridge rectifier is a negative DC outputterminal.
 7. The PFC apparatus of claim 1, wherein the DC rectificationcircuit comprises: a bridge rectifier, a first terminal of the bridgerectifier being coupled to the positive AC input terminal of the ACsource, a second terminal of the bridge rectifier being coupled to anegative AC input terminal of the AC source; a first reactance device, afirst terminal of the first reactance device being coupled to a thirdterminal of the bridge rectifier; a second reactance device, a firstterminal of the second reactance being coupled to a second terminal ofthe first reactance; and a third reactance device, a first terminal ofthe third reactance being coupled to a second terminal of the secondreactance, a second terminal of the third inductive reactance devicebeing coupled to a fourth terminal of the bridge rectifier.
 8. The PFCapparatus of claim 7, wherein the first reactance device is an inductor.9. The PFC apparatus of claim 7, wherein the second reactance device isa capacitor.
 10. The PFC apparatus of claim 7, wherein the thirdreactance device is an inductor.
 11. The PFC apparatus of claim 1,wherein the DC rectification circuit comprises: a bridge rectifier, afirst terminal of the bridge rectifier being coupled to the positive ACinput terminal of the AC source, a second terminal of the bridgerectifier being coupled to a negative AC input terminal of the ACsource; a first reactance device, a first terminal of the firstreactance device being coupled to a third terminal of the bridgerectifier; a second reactance device, a first terminal of the secondreactance being coupled to a second terminal of the first reactance; athird reactance device, a first terminal of the third reactance beingcoupled to a second terminal of the second reactance; a fourth reactancedevice, a first terminal of the fourth reactance device being coupled toa second terminal of the third reactance, the second terminal of thefourth reactance device being coupled to a fourth terminal of the bridgerectifier; and a switch, a first terminal of the switch being coupled tothe second terminal of the second inductive reactance device, a secondterminal of the switch being coupled to the negative AC input terminalof the AC source.
 12. The PFC apparatus of claim 11, wherein the firstreactance device is an inductor.
 13. The PFC apparatus of claim 11,wherein the second reactance device is a capacitor.
 14. The PFCapparatus of claim 11, wherein the third reactance device is acapacitor.
 15. The PFC apparatus of claim 11, wherein the fourthreactance device is an inductor.
 16. The PFC apparatus of claim 11,wherein the first and fourth inductive reactance devices comprise acouple choke.
 17. The PFC apparatus of claim 1, wherein the PFCauxiliary circuit comprises a resonant circuit, the resonant circuitcomprising: a third reactance device, a first terminal of the thirdreactance device being coupled to the positive AC input terminal; and afourth reactance device, a first terminal of the fourth reactance devicebeing coupled to a second terminal of the third reactance device, asecond terminal of the fourth inductive reactance device being coupledto the input terminal of the DC rectification circuit.
 18. The PFCapparatus of claim 17, wherein the PFC auxiliary circuit furthercomprises a second DC rectification, an input terminal of the second DCrectification being coupled to the second terminal of the fourthreactance, and a first output terminal of the second DC rectificationcircuit being coupled to the first output terminal of the DCrectification circuit, and a second output terminal of the second DCrectification circuit being coupled to the second output terminal of theDC rectification circuit.
 19. The PFC apparatus of claim 18, wherein thesecond DC rectification circuit is a first diode.
 20. The PFC apparatusof claim 19, wherein a first terminal of the first diode is an anode,and a second terminal of the first diode is a cathode.
 21. The PFCapparatus of claim 18, wherein the second DC rectification circuitfurther comprises a second diode, a first terminal of the second diodeis coupled to the first terminal of the first diode, and a secondterminal of the second diode is coupled to the second output terminal ofthe DC rectification circuit.
 22. The PFC apparatus of claim 21, whereina first terminal of the second diode is a cathode, and a second terminalof the second diode is an anode.
 23. The PFC apparatus of claim 17,wherein the third reactance device is an inductor.
 24. The PFC apparatusof claim 17, wherein the fourth reactance device is a capacitor.
 25. ThePFC apparatus of claim 17, wherein the third reactance device is aresistor.
 26. The PFC apparatus of claim 1, wherein the load is aresistor.
 27. The PFC apparatus of claim 1, wherein the load is anelectronic devices.